This invention relates to printer/copier systems and more specifically to systems employing an electrostatic printing process.
Electrostatic printer technology has previously involved the delivery of information to a photo conductive surface to form a latent electrostatic image which is then toned, physically moved, and electrostatically transferred to a contacting paper substrate. Such electrostatic printer technology has been embodied in several ways. Laser address printers utilize a laser to raster across a rotating photo-conductive drum to create a latent electrostatic image as the laser is modulated on and off, similar to a TV scan. The image is then toned and transferred as previously described. The major advantage of the laser system is speed, which can go up to several thousand lines per minute. However, it has several major disadvantages. The mechanical-optical interface is very complex, as is the latent image process, the physical size is quite large, and the cost is high.
The Dennison process of electrostatic printer technology utilizes an array of electrodes to write a latent image on a dielectric surface. In effect, the laser is replaced with an electrode system and the photoconductive surface replaced with ordinary dielectric. Most of the disadvantages are still present as the latent image process is retained, and in addition, the electrodes require high voltage to write on the dielectric. Since this method is not adaptable to integrated solid state technology for addressing the hundreds of electrodes, matrix addressing is required.
The Versatec printing method uses an electrode array to write a latent image on a dielectric layer, which is on the surface of a special paper. The latent image transfer process is done away with, but at the expense of requiring special paper. In a related application, Nelson teaches in U.S. Pat. No. 4,146,898 a magnetic tape on which information is recorded, the tape passed through a toner application where toner is attracted to the tape at the areas where magnetic information is recorded (latent magnetic image). The tape then moves to a transfer area where it passes between plain paper and two electrodes. A high potential is pulsed between the two electrodes to transfer the toner from the tape to the paper across an air gap.
Kilby, in U.S. Pat. No. 3,979,758, shows an electrostatic process where the addressable printhead creates a charge on small plates on the head. Toner is brushed across the head, and toner particles attracted by the charged plates form an image. The head is then moved and the toner transferred by contact to plain paper.
The toner required for each application described is, in most cases, specially made for that application. Generally, particles of the selected pigmented are subjected to a process which coats the particles of pigment with resin. The resin coating allows the particles to be electrically charged, and to be transferred from surface to surface until fixed on the desired surface by heat or other means presently used.